Message: Undefined property: Utilisateurs::$form_validation

im en train d'essayer de modifier mon application de base de données MySQL pour la base de données MongoDB. Mon projet nécessite de comparer les deux de ces, et mon code de MySQL a été de travail et maintenant, il me donne cette erreur.

Trace De La Pile:

Une Erreur PHP a été rencontrée Gravité: Message notice: Undefined property: Users::$form_validation nom de fichier: controllers/users.php Numéro de Ligne: 26

Ligne d'erreur:

$this->form_validation->set_rules('username','Username','trim|required|min_length[4]|xss_clean');   

Code:

<?php
class Users extends CI_Controller{
public function register(){ 
$this->form_validation->set_rules('first_name','First Name','trim|required|max_length[50]|min_length[2]|xss_clean');
$this->form_validation->set_rules('last_name','Last Name','trim|required|max_length[50]|min_length[2]|xss_clean');
$this->form_validation->set_rules('email','Email','trim|required|max_length[100]|min_length[5]|xss_clean|valid_email');
$this->form_validation->set_rules('username','Username','trim|required|max_length20]|min_length[6]|xss_clean');
$this->form_validation->set_rules('password','Password','trim|required|max_length[20]|min_length[6]|xss_clean');
$this->form_validation->set_rules('password2','Confirm Password','trim|required|max_length[50]|min_length[2]|xss_clean|matches[password]');
if($this->form_validation->run() == FALSE){
$data['main_content']='users/register';
$this->load->view('layouts/main',$data);    
}else{
if($this->User_model->create_member()){ 
$this->session->set_flashdata('registered','Registered successfully');
redirect('home/index'); 
}
}
}
public function login(){
//$this->load->model('user_model');
$this->form_validation->set_rules('username','Username','trim|required|min_length[4]|xss_clean');      
$this->form_validation->set_rules('password','Password','trim|required|min_length[4]|max_length[50]|xss_clean');        
$collection = $this->database->users;
if($this->form_validation->run() == FALSE){
$this->session->set_flashdata('login_failed', 'Sorry, this username doesn't exist.');
redirect('home/index');
} else {
$username=$_POST['login'];
$password=$_POST['password'];
$user_id = $collection->findOne(array('username' => $username, 'password' => md5($password)));
//$username = $this->input->post('username');
//$password = $this->input->post('password');
$user_id = $this->User_model->login_user($username,$password);
if($user_id){
$user_data = array(
'user_id'   => $user_id,
'username'  => $username,
'logged_in' => true
);
$this->session->set_userdata($user_data);
redirect('home/index');
} else {
$this->session->set_flashdata('login_failed', 'Sorry, this username doesn't exist.');
redirect('home/index');
}
}
}
public function logout(){
$this->session->unset_userdata('logged_in');
$this->session->unset_userdata('user_id');
$this->session->unset_userdata('username');
$this->session->sess_destroy();
redirect('home/index');
}
}